OVLK

[Dustin Dudley]

Once my system has entered OVLK, I understand that this is a protective scenario brought about by one of my cells (banks) exceeding the intended state of charge. However, it has been shut down for several hours at this point. I have no way of knowing the SOC of cell (bank)1 at this point. Inverter works if I start the generator, so that's not the issue. 

Do I need to (1) unplug the SBMS0 and reconnect it; (2) just wait; or (3) something else?

[Dacian Todea (electrodacus)]

OVLK will be cleared once all cells drop below the over voltage recovery limit (if is LiFePO4 and default settings it will be below 3.4V).

But there will be no reason for any cell to trigger the over voltage lock witch is set by default at 3.75V that is 200mV above 3.55V where charger should have stopped if all worked correctly.

[sailingharry]

As Dacian has pointed out, OVLK (and UVLK) are disaster conditions that should never be reached.  However, as you've discovered, if it happens it presents a small issue -- it's VERY hard to undo the LOCK.  I've triggered a UVLK (LVLK?  I forget the name) twice on my boat (somewhat intentionally).  Once the lock has been triggered, the only way to charge it (to undo a UVLK) or discharge it (to undo a UVLK) is to manually bypass the BMS and directly control the main disconnect.  On my boat, the disconnect has that built in (an override knob), so if I dig down under the bed (and piles of gear!) where that is hidden, I can turn the knob.  I think I still need to bypass other safeties to enable charging, but I forget.

In your case, to get the voltage down from the OVLK, you'll need to find a way to discharge, and if OVLK is anything like UVLK it's more than a little (if I recall, it took 50-100 Ah of charging to clear my UVLK).  You'll probably need to discharge at least 5-10% of battery capacity to get it to reset.  You can use jumper cables from the battery side of the disconnect to the inverter (and also ensure the inverter is in a "allow to invert" mode).  It will take some understanding of the system (but at least you designed and built it!), but you can probably cobble together a load.

[Dave McCampbell]

Harry,
From reading Dacian's post on this above, for an OVLK, it appears that once all cells fall below 3.4vpc the OVLK will be cleared automatically.  After a full charge my cells rest at roughly 3.3vpc with no charge or load.  So that should clear an OVLK within a relatively short time with no further action by me.  An  UVLK will probably require active intervention by me, but still rather simple if you have separate charge and load busses.  If so, charging the cells should still be available until the UVLK is cleared.  Am I missing something here?

[Dacian Todea (electrodacus)]

Dave,

Both UVLK and OVLK are fault condition (not normal operation) and if they happen something needs to be done about that so it will not happen again.

In the case of OVLK most probable cause is bad connections between cells or cells not capable of handling the high charge current. Or it could be a charger that fails to stop for some reason (incorrect installation) shorted remote control wires or failed charger.

For UVLK same possibility of bad connection between cells or cells not capable to handle a high load. Or Loads not controlled by the SBMS that should be removed or setup with remote ON/OFF else they will damage the battery.

In correct installation neither UVLK or OVLK will happen as if battery is drained fully to UV 2.8V it will recover above 3V after all loads are correctly disconnect by SBMS0 and the SBMS0 self consumption that it is no problem for a day or two until solar is available to charge it. To get to 2.5V after a full discharge with just the SBMS0 as a load should require multiple weeks with no charge source (not the case if there is any solar panel connected).

When UVLK or OVLK is set both charge and discharge is disabled in order to try and protect the battery. There where cases in the past when people connected and inverter charger but controlled ON/OFF just the inverter and thus battery was overcharged triggering the OVLK and by allowing SBMS0 to turn OFF both charge sources and Loads in case of OVLK could save the battery from damage as turning OFF the inverter will usually mean also the grid charger will be turned OFF.

UV and OV are normal operation UVLK and OVLK are not.  For extra protection and EXT IOx set as type 5 (reacting in case of OVLK or UVLK) could trip one or more circuit breakers fully isolating the battery. This full battery isolation can include powering OFF the SBMS0 also.

I have batteries for 14 years more than a decade since I use some version of SBMS and I never had an OVLK or UVLK condition on any of my systems.  Even normal UV (empty battery) happen less than 3 times in this period.

[sailingharry]

Dacian covered a lot.  A couple of additional comments:

*  I have both a Charge and Discharge bus (but not really -- which bus is the Inverter/Charger?).  But since I am mostly autonomous and when cruising rarely use shore power, I mostly get the SBMS0 benefits of dual shunts.

*  A UVLK or OVLK trips BOTH contactors, as Dacian points out.

*  Once the UVLK trips, it also disables charge sources.  Both OVLK and UVLK are disaster conditions, and SMBS0 issues a "stop everything, everywhere, right now" command!  This is a little counterintuitive (why disable charge sources when your problem is needing charge?), but reflects the extreme rarity and major red flag of a OVLK/UVLK.

*  To recover from my UVLK (which, to repeat, was done somewhat intentionally -- I wanted to observe actions), I had to manually switch my contactors on (EGIS contactors similar to Blue Seas RBS).  Then, I had to jumper my Battery Protect (the "switch" for my solar panels) to allow them to charge.  This would also bring my Watt&Sea and my multivoltage charger (Centaur) online if they were available.  My other charge sources (MultiPlus and alternators) are much harder to disable the SMBS0 shutdown.  It would be worth thinking about how to easily bypass all SMBS0 shutdowns to make recovery easier.

*  In the case of OP's OV, I'm not sure a LFP battery "settles" like lead does.  I suspect a OV will stay high for an extended period unless somehow charge is bleed off.  But I have no experience in that area.